char *max_time(char *t1, char *t2) {
    if (t1 == NULL && t2 == NULL) {
        fprintf(stderr, "t1, t2 are null");
        exit(1);
    }

    if (t1 == NULL) {
        return t2;
    } else if (t2 == NULL) {
        return t1;
    }


    printf("Incoming time1: %s, size: %zun", t1, strlen(t1));
    printf("Incoming time2: %s, size: %zun", t2, strlen(t2));

    struct tm tm1, tm2;
    time_t time1, time2;
    double diff;

    memset(&tm1, 0, sizeof(struct tm));
    memset(&tm2, 0, sizeof(struct tm));
    memset(&time1, 0, sizeof(struct tm));
    memset(&time2, 0, sizeof(struct tm));

    strptime(t1, "%a, %d %b %Y %X %Z", &tm1);
    strptime(t2, "%a, %d %b %Y %X %Z", &tm2);
    time1 = mktime(&tm1);
    time2 = mktime(&tm2);

    /* debug */
    char str1[50];
    char str2[50];
    strftime(str1, 50, "%a, %d %b %Y %X %Z", &tm1);
    strftime(str2, 50, "%a, %d %b %Y %X %Z", &tm2);
    printf("Time1: %sn", str1);
    printf("Time2: %sn", str2);
    /* end debugging */


    diff = difftime(time1, time2);
    printf("Time diff: %fn", diff);
    if (diff > 0) {
        return t1;
    } else {
        return t2;
    }
}

char *t1[] = {"Tue, 27 Mar 2018 04:46:22 GMT",
                  "Tue, 27 Mar 2018 04:47:46 GMT",
                  "Tue, 27 Mar 2018 04:57:17 GMT",
                  "Tue, 27 Mar 2018 04:49:31 GMT",
                  "Tue, 27 Mar 2018 04:48:46 GMT",
                  "Mon, 26 Mar 2018 03:44:55 GMT"};

    int i = 0;
    char *res = NULL;
    for(i = 0; i < 5; i++) {
        res = max_time(res, t1[i]);
        printf("Res: %sn", res);
    }